smarty156 Posted November 2, 2018 Report Share Posted November 2, 2018 My money is on sheared flywheel key. I had exactly what you describe and that's what it was. Quote Link to comment Share on other sites More sharing options...
dakh Posted November 2, 2018 Author Report Share Posted November 2, 2018 4 hours ago, smarty156 said: My money is on sheared flywheel key. I had exactly what you describe and that's what it was. Got it, thank you. Good to know! Was your case also runaway diesel when running out of gas or some other way you managed to get the key snapped? What was the remedy -- just a new key or you had to get a new flywheel too? I'm assuming crank end is the toughest part in the whole deal. Ah what the heck I need to stop posting and open it up and take a look. Quote Link to comment Share on other sites More sharing options...
Jeff B Posted November 3, 2018 Report Share Posted November 3, 2018 The key may not be that big of a deal. Most mfg use a keyway for fast assembly. A lot of after market ignitions do not use a key. You set the timing and tighten the nut on the tapered shaft and you are good to go. My vintage Husky has an ignition that does not key. I am saying just in case the key slot is screwed up. Jeff Quote Link to comment Share on other sites More sharing options...
v1nn1e Posted December 2, 2018 Report Share Posted December 2, 2018 Just stumbled across this topic by chance but read the original first post and had almost exactly the same thing on my Sherco 2T. I also pulled the plug cap off the spark plug and the engine stopped shortly after that. I put my runaway down to an intermittent carb fault, where I'm seeing it flood. Reckoned it was excess build up of fuel in the crank somehow, self-igniting off the plug in some way or other. Anyway, subsequently I can't get any spark from the ignition system (all Leonelli) and spoke to Bradford Ignitions/Motoplat and he reckoned pulling the spark plug cap was a sure way to fry the CDI unit. But, it sounds like folks have done that and their CDI's have survived? Were they Leonelli? Maybe GasGas use Hydria and they are more robust? Thanks for reading Quote Link to comment Share on other sites More sharing options...
dakh Posted July 25, 2019 Author Report Share Posted July 25, 2019 Sorry for lack of updates, had limited time to work on bikes and had to dedicate all of it to keeping my enduro bike going. Finally took a look at this pos Contact ES. Turned out I have left hand thread flywheel puller but needed a right hand so waiting on that to show up to see if the flywheel got spun. Pulled exhaust and then had to pull the head off and now need to pull cylinder off to see if the crank is dead too. Sorry my terminology might be off, I know my 4-stroke Honda CRFs in and out but clueless on 2-strokes. Head looks good. So I'm now wondering did it spin fast enough while in the "diesel" mode to do this damage or it was some manufacturing defect that was there all along? And also still how do I prevent it from doing this trick again. Quote Link to comment Share on other sites More sharing options...
d2w Posted July 25, 2019 Report Share Posted July 25, 2019 (edited) Dakh - excuse my old eyes and it's early morning here now, but - in the (first) photo taken through the exhaust outlet, is the ring retaining pin visible in the groove of the upper ring? The ends of those rings look too well define. There should be no ring ends visible in that area of the piston. To me it looks like the piston was installed backwards and the ring ends caught on the exhaust port. Ensure that your piston is correctly oriented; the manufacturing "arrow" should point to the exhaust port (and the ring retaining pins and ring ends should not pass over any open areas of the cylinder). And to me, the second picture seems to show that the wear was occurring over a longer period of time - as evidenced by the variations in the black and brown areas - and that it didn't just "grenade". I think something was rubbing on the cylinder that shouldn't have. Edited July 25, 2019 by d2w Quote Link to comment Share on other sites More sharing options...
dakh Posted July 25, 2019 Author Report Share Posted July 25, 2019 Ring gaps look to be in the right place (it's the back of the cylinder), it was just enough piston material that obliterated the ring -- I scraped it off with a knife and it's as expected. Cylinder is definitely toast too, the scrape that is above the port maybe can be cleaned up and honed out but there's a good chunk of coating (nicasil?) missing below the port that I uncovered after I scraped some of the aluminum. Maybe it was an imperfection in the cylinder to begin with. But looking at the exhaust side of the piston, it has perceptible scrapes all along the surface so this thing just ran way too hot. At least the crank and rod look Ok, no play at all. Should I send this cylinder to Millenium or someone like that or just get a new one? Good source for pistons? One more thing, while the bike was parked it weeped a bit of coolant. I could not trace where it came from. Took the water pump out and it looks all good to me. Is that maybe expected or should I try to maybe pressure test the cooling system? It didn't leak anymore so I'm not able to reproduce it. Radiator with no cap that would blow pressure off freaks me out a bit, if it got so hot maybe there's damage that I'm not able to see? Thanks! Quote Link to comment Share on other sites More sharing options...
sherco70 Posted August 17, 2019 Report Share Posted August 17, 2019 I have read that plugging the exhaust will stop the engine, but have no experience with this personally. Art Quote Link to comment Share on other sites More sharing options...
dakh Posted August 27, 2019 Author Report Share Posted August 27, 2019 (edited) Update: put a new (well, rebuilt by Millenium Tech) cylinder and piston on, bike started right up. I had kill switch disconnected (while I was messing around trying to understand why it doesn't run) so right away I had a chance to practice choking it. Shop towel up the exhaust pipe or a shoe trying to block it would not kill the bike, not even close. So I think my algo if this crap happens again is to just put it in gear and release the clutch. Maybe not drop it to not do any damage but act quick and get it done. Edited August 27, 2019 by dakh Quote Link to comment Share on other sites More sharing options...
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